Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$133.74	4.440%	$139.6781	$139.68	$139.70	$139.70
Purchase #2	$150.43	9.138%	$164.1763	$164.18	$164.20	$164.20
Purchase #3	$35.71	4.714%	$37.3934	$37.39	$37.40	$37.40
Purchase #4	$157.93	6.822%	$168.704	$168.70	$168.70	$168.70
Purchase #5	$129.92	4.772%	$136.1198	$136.12	$136.10	$136.10
Purchase #6	$48.68	10.343%	$53.715	$53.72	$53.70	$53.70
Purchase #7	$90.52	9.720%	$99.3185	$99.32	$99.30	$99.30
7 purchase totals =	$746.93		$799.1051	$799.11	$799.10	$799.10